Drools推理的例子1－房间救火

 1.必须使用有状态的session

KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();kbuilder.add( ResourceFactory.newClassPathResource( "fireAlarm.drl", getClass() ),              ResourceType.DRL );if ( kbuilder.hasErrors() ) {    System.err.println( builder.getErrors().toString() );}kbase.addKnowledgePackages( kbuilder.getKnowledgePackages() );StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();

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2.基本类

• Room类
• Sprinkler灭火器
• Alarm报警器
• Fire火灭

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3.规则写法

注意

a.modify语句，是对对象的修改，与直接调用对象的set方法的不同是，调用modify后，被修改的对象会在规则引擎中重新检查是否匹配某条规则，从而产生推理。因此，推理必须使用有状态的session

b."not"语句，可以检查一个对象是否不存在

//房间有火灭时，打开灭火器rule "When there is a fire turn on the sprinkler"when Fire($room : room) $sprinkler : Sprinkler( room == $room, on == false )then modify( $sprinkler ) { setOn( true ) }; System.out.println( "Turn on the sprinkler for room " + $room.getName() );end//房间没有火时，如果灭火器还开着，则关闭灭火器rule "When the fire is gone turn off the sprinkler"when $room : Room( ) $sprinkler : Sprinkler( room == $room, on == true ) not Fire( room == $room )then modify( $sprinkler ) { setOn( false ) }; System.out.println( "Turn off the sprinkler for room " + $room.getName() );end

只要有任意一个房间发生火灭，就打开报警器

注意这里是用的exists语句，检查对象是否存在

rule "Raise the alarm when we have one or more fires"when exists Fire()then insert( new Alarm() ); System.out.println( "Raise the alarm" );end

当所有房间都不存在火灭时，关闭报警器

rule "Cancel the alarm when all the fires have gone"when not Fire() $alarm : Alarm()then retract( $alarm ); System.out.println( "Cancel the alarm" );end

当不存在火灭以及报警时，报告一切安好！

rule "Status output when things are ok"when not Alarm() not Sprinkler( on === true ) then System.out.println( "Everything is ok" );end

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4.规则执行过程

a. 准备4个房间，并先触发一次执行

String[] names = new String[]{"kitchen", "bedroom", "office", "livingroom"};Map<String,Room> name2room = new HashMap<String,Room>();for( String name: names ){ Room room = new Room( name ); name2room.put( name, room ); ksession.insert( room );//insert时，已经完成规则的匹配 Sprinkler sprinkler = new Sprinkler( room ); ksession.insert( sprinkler );}ksession.fireAllRules();//触发规则的执行

系统报“Everything is ok！”

b.两个房间发生火灭

Fire kitchenFire = new Fire( name2room.get( "kitchen" ) );Fire officeFire = new Fire( name2room.get( "office" ) );FactHandle kitchenFireHandle = ksession.insert( kitchenFire );FactHandle officeFireHandle = ksession.insert( officeFire );ksession.fireAllRules();

系统报“Raise the alarm”  “Turn on the sprinkler for room kitchen”  “Turn on the sprinkler for room office”

c.把Fire对象移除掉

ksession.retract( kitchenFireHandle );ksession.retract( officeFireHandle );ksession.fireAllRules();

系统报“Cancel the alarm”  “Everything is ok”